1. Field of the Invention
The present invention relates in general to an internal combustion engine and in particular to a fuel supply system of an internal combustion engine.
2. Description of Related Art
A fuel supply system of an outboard motor's internal combustion engine typically includes an external supply fuel tank and a plurality of low-pressure fuel pumps that transfer fuel from the supply fuel tank to a delivery fuel tank located in the power head of the outboard motor. The fuel supply system also includes a high-pressure fuel pump that transfers fuel from the delivery fuel tank to the engine. The low-pressure fuel pump often is a diaphragm valve operated by the camshaft of the engine so that when the camshaft rotates, the valve moves. Alternatively, with a two-stroke, crankcase compression engine, a pressure fluctuation in an associated crankcase chamber drives the diaphragm valve. The valve's diaphragm movement causes the pressure in the pump to change, causing fuel to be pumped from the external supply tank to the delivery tank.
Diaphragm fuel pumps, however, suffer from a number of drawbacks. For instance, one drawback of diaphragm fuel pump is that the diaphragm tends to wear out. The diaphragm valve moves continuously as the camshaft rotates, or the pressure within the associated crankcase chamber fluctuates, regardless of the fuel needs of the delivery tank. The constant movement of the diaphragm causes the diaphragm to fatigue.
Diaphragm pumps also often fail to produce enough pressure to deliver a sufficient amount of fuel to the delivery tank when the engine runs for an extended period of time under high-fuel consumption conditions. If the delivery tank does not receive a sufficient amount of fuel from the low-pressure pump, the high-pressure pump will run dry. Running the pump dry damages the pump. An insufficient amount of fuel in the delivery tank also prevents the engine from receiving the desired amount of fuel. This affects the fuel/air ratio of the fuel charge delivered to the engine and can cause the engine to stall.
In an effort to supply the delivery tank with a sufficient amount of fuel, fuel supply systems commonly include several low-pressure diaphragm pumps. Multiple low-pressure fuel pumps, however, increase the size of the engine and overly complicate the arrangement and plumbing of the fuel delivery system.
The diaphragm valve in each of the pumps is made relatively large in order to produce enough pressure to deliver a sufficient volume of fuel to the delivery tank. The pump body also has a large size because it must accommodate the large diaphragm valve. Multiple, large low-pressure pumps increase the size of the power head. The power head of the outboard motor generally extends above the transom of the watercraft and, consequently, the power head produces aerodynamic drag on the watercraft as the watercraft speeds over the water. The size and shape of the power head directly affects the amount of drag produced. Thus, multiple, large low-pressure fuel pumps negatively increase the drag experienced by the outboard motor.
Another problem with multiple low-pressure fuel pumps is they tend to make the fuel supply system complicated. Each low-pressure fuel pump includes an inlet port and outlet port that communicates with a respective conduit. A fitting is provided for each port to ensure that the respective conduit is sealingly engaged with the port. Thus, the multiple low-pressure fuel pumps include two sets of conduits, a set of conduits leading to the low-pressure fuel pumps and a set leading from the fuel pumps. A connector arrangement is provided for each set of multiple conduits for merging the set of conduits into a single conduit. Each connector arrangement requires multiple fittings to ensure that the conduits sealingly engage the connector arrangement. The complex nature of this arrangement makes the arrangement difficult and expensive to assemble. The complex arrangement is also susceptible to fuel leakage because of the multitude of fluid connections in the arrangement.